RFR: 8203352: Improve java implementation of Integer/Long.numberOfLeadingZeros (original) (raw)

Claes Redestad claes.redestad at oracle.com
Fri May 18 19:05:29 UTC 2018

On 2018-05-18 20:23, Ivan Gerasimov wrote:

Another approach may be to just delegate to Integer.numberOfLeadingZeros() like this:

public static int numberOfLeadingZeros(long i) { int x = (int)(i >>> 32); return x == 0 ? 32 + Integer.numberOfLeadingZeros((int)i) : Integer.numberOfLeadingZeros(x); }

I'm partial to the simplicity of this solution - whether or not there are platforms where 64-bit lz instruction is missing. It's very slightly slower than baseline for -Xint, but markedly faster when C1-compiled, which I think weighs heavier.

http://cr.openjdk.java.net/~redestad/8203352/open.01/

/Claes

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